/**
 *    Copyright 2009-2015 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.builder.xml;

import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;

import javax.sql.DataSource;

import org.apache.ibatis.builder.BaseBuilder;
import org.apache.ibatis.builder.BuilderException;
import org.apache.ibatis.datasource.DataSourceFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.loader.ProxyFactory;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.mapping.DatabaseIdProvider;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.parsing.XNode;
import org.apache.ibatis.parsing.XPathParser;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.reflection.MetaClass;
import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;
import org.apache.ibatis.session.AutoMappingBehavior;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.LocalCacheScope;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.type.JdbcType;

/**
 * @author Clinton Begin
 */
/**
 * XML配置构建器，建造者模式,继承BaseBuilder
 *
 */
public class XMLConfigBuilder extends BaseBuilder {

	/**
	 * 是否已解析，XPath解析器,环境
	 */
	private boolean parsed;
	/**
	 * XPath解析器,用来解析xml文件的 包括检测xml文件格式
	 */
	private XPathParser parser;
	/**
	 * 数据源环境 --加载哪种环境(开发环境/生产环境)
	 */
	private String environment;

	// 以下3个一组
	/**
	 * 构造XML配置构建器
	 * 
	 * @param reader
	 *            操作字符流的类
	 */
	public XMLConfigBuilder(Reader reader) {
		this(reader, null, null);
	}

	/**
	 * 构造XML配置构建器
	 * 
	 * @param reader
	 *            操作字符流的类
	 * @param environment
	 *            数据源环境 --加载哪种环境(开发环境/生产环境)
	 */
	public XMLConfigBuilder(Reader reader, String environment) {
		this(reader, environment, null);
	}

	/**
	 * 构造XML配置构建器
	 * 
	 * @param reader
	 *            操作字符流的类
	 * @param environment
	 *            数据源环境 --加载哪种环境(开发环境/生产环境)
	 * @param props
	 *            properties元素集
	 */
	// 构造函数，转换成XPathParser再去调用构造函数
	public XMLConfigBuilder(Reader reader, String environment, Properties props) {
		// 构造一个需要验证，XMLMapperEntityResolver的XPathParser
		this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
	}

	// 以下3个一组
	/**
	 * 构造XML配置构建器
	 * 
	 * @param inputStream
	 *            操作字节流的类
	 */
	public XMLConfigBuilder(InputStream inputStream) {
		this(inputStream, null, null);
	}

	/**
	 * 构造XML配置构建器
	 * 
	 * @param inputStream
	 *            操作字节流的类
	 * @param environment
	 *            数据源环境 --加载哪种环境(开发环境/生产环境)
	 */
	public XMLConfigBuilder(InputStream inputStream, String environment) {
		this(inputStream, environment, null);
	}

	/**
	 * 构造XML配置构建器
	 * 
	 * @param inputStream
	 *            操作字节流的类
	 * @param environment
	 *            数据源环境 --加载哪种环境(开发环境/生产环境)
	 * @param props
	 *            properties元素集
	 */
	public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
		this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
	}

	/**
	 * 构造XML配置构建器
	 * 
	 * @param parser
	 *            解析器
	 * @param environment
	 *            数据源环境 --加载哪种环境(开发环境/生产环境)
	 * @param props
	 *            properties元素集
	 */
	// 上面6个构造函数最后都合流到这个函数，传入XPathParser
	private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
		// 首先调用父类初始化Configuration
		super(new Configuration());
		// 错误上下文设置成SQL Mapper Configuration(XML文件配置),以便后面出错了报错用吧
		ErrorContext.instance().resource("SQL Mapper Configuration");
		// 将Properties全部设置到Configuration里面去
		this.configuration.setVariables(props);
		this.parsed = false;
		this.environment = environment;
		this.parser = parser;
	}

	/**
	 * 解析
	 * @return Configuration
	 */
	// 解析配置
	public Configuration parse() {
		// 如果已经解析过了，报错
		if (parsed) {
			throw new BuilderException("Each XMLConfigBuilder can only be used once.");
		}
		parsed = true;
		// <?xml version="1.0" encoding="UTF-8" ?>
		// <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
		// "http://mybatis.org/dtd/mybatis-3-config.dtd">
		// <configuration>
		// <environments default="development">
		// <environment id="development">
		// <transactionManager type="JDBC"/>
		// <dataSource type="POOLED">
		// <property name="driver" value="${driver}"/>
		// <property name="url" value="${url}"/>
		// <property name="username" value="${username}"/>
		// <property name="password" value="${password}"/>
		// </dataSource>
		// </environment>
		// </environments>
		// <mappers>
		// <mapper resource="org/mybatis/example/BlogMapper.xml"/>
		// </mappers>
		// </configuration>

		// 根节点是configuration
		parseConfiguration(parser.evalNode("/configuration"));
		return configuration;
	}

	// 解析配置
	/**
	 * 解析配置
	 * @param root this.document 当前xml文档
	 */
	private void parseConfiguration(XNode root) {
		try {
			// 分步骤解析
			// issue #117 read properties first
			// 1.properties
			propertiesElement(root.evalNode("properties"));
			// 2.类型别名
			typeAliasesElement(root.evalNode("typeAliases"));
			// 3.插件
			pluginElement(root.evalNode("plugins"));
			// 4.对象工厂
			objectFactoryElement(root.evalNode("objectFactory"));
			// 5.对象包装工厂
			objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
			// 6.设置
			settingsElement(root.evalNode("settings"));
			// read it after objectFactory and objectWrapperFactory issue #631
			// 7.环境
			environmentsElement(root.evalNode("environments"));
			// 8.databaseIdProvider
			databaseIdProviderElement(root.evalNode("databaseIdProvider"));
			// 9.类型处理器
			typeHandlerElement(root.evalNode("typeHandlers"));
			// 10.映射器
			mapperElement(root.evalNode("mappers"));
		} catch (Exception e) {
			throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
		}
	}

	// 2.类型别名
	// <typeAliases>
	// <typeAlias alias="Author" type="domain.blog.Author"/>
	// <typeAlias alias="Blog" type="domain.blog.Blog"/>
	// <typeAlias alias="Comment" type="domain.blog.Comment"/>
	// <typeAlias alias="Post" type="domain.blog.Post"/>
	// <typeAlias alias="Section" type="domain.blog.Section"/>
	// <typeAlias alias="Tag" type="domain.blog.Tag"/>
	// </typeAliases>
	// or
	// <typeAliases>
	// <package name="domain.blog"/>
	// </typeAliases>
	/**
	 * 解析 typeAliases<类型别名元素>
	 * @param parent 父节点
	 */
	private void typeAliasesElement(XNode parent) {
		if (parent != null) {
			for (XNode child : parent.getChildren()) {
				if ("package".equals(child.getName())) {
					// 如果是package
					String typeAliasPackage = child.getStringAttribute("name");
					// （一）调用TypeAliasRegistry.registerAliases，去包下找所有类,然后注册别名(有@Alias注解则用，没有则取类的simpleName)
					configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
				} else {
					// 如果是typeAlias
					String alias = child.getStringAttribute("alias");
					String type = child.getStringAttribute("type");
					try {
						Class<?> clazz = Resources.classForName(type);
						// 根据Class名字来注册类型别名
						// （二）调用TypeAliasRegistry.registerAlias
						if (alias == null) {
							// alias可以省略
							typeAliasRegistry.registerAlias(clazz);
						} else {
							typeAliasRegistry.registerAlias(alias, clazz);
						}
					} catch (ClassNotFoundException e) {
						throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
					}
				}
			}
		}
	}

	// 3.插件
	// MyBatis 允许你在某一点拦截已映射语句执行的调用。默认情况下,MyBatis 允许使用插件来拦截方法调用
	// <plugins>
	// <plugin interceptor="org.mybatis.example.ExamplePlugin">
	// <property name="someProperty" value="100"/>
	// </plugin>
	// </plugins>
	/**
	 * 解析plugins<插件元素>
	 * @param parent 父节点
	 * @throws Exception
	 */
	private void pluginElement(XNode parent) throws Exception {
		if (parent != null) {
			for (XNode child : parent.getChildren()) {
				String interceptor = child.getStringAttribute("interceptor");
				Properties properties = child.getChildrenAsProperties();
				Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
				interceptorInstance.setProperties(properties);
				// 调用InterceptorChain.addInterceptor
				configuration.addInterceptor(interceptorInstance);
			}
		}
	}

	// 4.对象工厂,可以自定义对象创建的方式,比如用对象池？
	// <objectFactory type="org.mybatis.example.ExampleObjectFactory">
	// <property name="someProperty" value="100"/>
	// </objectFactory>
	/**
	 * 解析objectFactory<对象工厂>
	 * @param context  当前指向的节点<节点内容>如:objectFactory
	 * @throws Exception
	 */
	private void objectFactoryElement(XNode context) throws Exception {
		if (context != null) {
			String type = context.getStringAttribute("type");
			Properties properties = context.getChildrenAsProperties();
			ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();
			factory.setProperties(properties);
			configuration.setObjectFactory(factory);
		}
	}

	// 5.对象包装工厂
	/**
	 * 解析对象包装工厂
	 * @param context 当前指向的节点<节点内容>如:objectWrapperFactory
	 * @throws Exception
	 */
	private void objectWrapperFactoryElement(XNode context) throws Exception {
		if (context != null) {
			String type = context.getStringAttribute("type");
			ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();
			configuration.setObjectWrapperFactory(factory);
		}
	}

	// 1.properties
	// <properties resource="org/mybatis/example/config.properties">
	// <property name="username" value="dev_user"/>
	// <property name="password" value="F2Fa3!33TYyg"/>
	// </properties>
	/**
	 * 解析properties元素
	 * @param context 当前指向的节点<节点内容>如:properties
	 * @throws Exception
	 */
	private void propertiesElement(XNode context) throws Exception {
		if (context != null) {
			// 如果在这些地方,属性多于一个的话,MyBatis 按照如下的顺序加载它们:

			// 1.在 properties 元素体内指定的属性首先被读取。
			// 2.从类路径下资源或 properties 元素的 url 属性中加载的属性第二被读取,它会覆盖已经存在的完全一样的属性。
			// 3.作为方法参数传递的属性最后被读取, 它也会覆盖任一已经存在的完全一样的属性,这些属性可能是从 properties
			// 元素体内和资源/url 属性中加载的。
			// 传入方式是调用构造函数时传入，public XMLConfigBuilder(Reader reader, String
			// environment, Properties props)

			// 1.XNode.getChildrenAsProperties函数方便得到孩子所有Properties
			Properties defaults = context.getChildrenAsProperties();
			// 2.然后查找resource或者url,加入前面的Properties
			String resource = context.getStringAttribute("resource");
			String url = context.getStringAttribute("url");
			if (resource != null && url != null) {
				throw new BuilderException(
						"The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other.");
			}
			if (resource != null) {
				defaults.putAll(Resources.getResourceAsProperties(resource));
			} else if (url != null) {
				defaults.putAll(Resources.getUrlAsProperties(url));
			}
			// 3.Variables也全部加入Properties
			Properties vars = configuration.getVariables();
			if (vars != null) {
				defaults.putAll(vars);
			}
			parser.setVariables(defaults);
			configuration.setVariables(defaults);
		}
	}

	// 6.设置
	// 这些是极其重要的调整, 它们会修改 MyBatis 在运行时的行为方式
	// <settings>
	// <setting name="cacheEnabled" value="true"/>
	// <setting name="lazyLoadingEnabled" value="true"/>
	// <setting name="multipleResultSetsEnabled" value="true"/>
	// <setting name="useColumnLabel" value="true"/>
	// <setting name="useGeneratedKeys" value="false"/>
	// <setting name="enhancementEnabled" value="false"/>
	// <setting name="defaultExecutorType" value="SIMPLE"/>
	// <setting name="defaultStatementTimeout" value="25000"/>
	// <setting name="safeRowBoundsEnabled" value="false"/>
	// <setting name="mapUnderscoreToCamelCase" value="false"/>
	// <setting name="localCacheScope" value="SESSION"/>
	// <setting name="jdbcTypeForNull" value="OTHER"/>
	// <setting name="lazyLoadTriggerMethods"
	// value="equals,clone,hashCode,toString"/>
	// </settings>
	/**
	 * 解析settings元素
	 * @param context 当前指向的节点<节点内容>如:settings
	 * @throws Exception 
	 */
	private void settingsElement(XNode context) throws Exception {
		if (context != null) {
			Properties props = context.getChildrenAsProperties();
			// Check that all settings are known to the configuration class
			// 检查下是否在Configuration类里都有相应的setter方法（没有拼写错误）
			MetaClass metaConfig = MetaClass.forClass(Configuration.class);
			for (Object key : props.keySet()) {
				if (!metaConfig.hasSetter(String.valueOf(key))) {
					throw new BuilderException("The setting " + key
							+ " is not known.  Make sure you spelled it correctly (case sensitive).");
				}
			}

			// 下面非常简单，一个个设置属性
			// 如何自动映射列到字段/ 属性
			configuration.setAutoMappingBehavior(
					AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
			// 缓存
			configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
			// proxyFactory (CGLIB | JAVASSIST)
			// 延迟加载的核心技术就是用代理模式，CGLIB/JAVASSIST两者选一
			configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
			// 延迟加载
			configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
			// 延迟加载时，每种属性是否还要按需加载
			configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), true));
			// 允不允许多种结果集从一个单独 的语句中返回
			configuration
					.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
			// 使用列标签代替列名
			configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
			// 允许 JDBC 支持生成的键
			configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
			// 配置默认的执行器
			configuration
					.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
			// 超时时间
			configuration
					.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
			// 是否将DB字段自动映射到驼峰式Java属性（A_COLUMN-->aColumn）
			configuration
					.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
			// 嵌套语句上使用RowBounds
			configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
			// 默认用session级别的缓存
			configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
			// 为null值设置jdbctype
			configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
			// Object的哪些方法将触发延迟加载
			configuration.setLazyLoadTriggerMethods(
					stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
			// 使用安全的ResultHandler
			configuration
					.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
			// 动态SQL生成语言所使用的脚本语言
			configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
			// 当结果集中含有Null值时是否执行映射对象的setter或者Map对象的put方法。此设置对于原始类型如int,boolean等无效。
			configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
			// logger名字的前缀
			configuration.setLogPrefix(props.getProperty("logPrefix"));
			// 显式定义用什么log框架，不定义则用默认的自动发现jar包机制
			configuration.setLogImpl(resolveClass(props.getProperty("logImpl")));
			// 配置工厂
			configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
		}
	}

	// 7.环境
	// <environments default="development">
	// <environment id="development">
	// <transactionManager type="JDBC">
	// <property name="..." value="..."/>
	// </transactionManager>
	// <dataSource type="POOLED">
	// <property name="driver" value="${driver}"/>
	// <property name="url" value="${url}"/>
	// <property name="username" value="${username}"/>
	// <property name="password" value="${password}"/>
	// </dataSource>
	// </environment>
	// </environments>
	/**
	 * 解析environments元素
	 * @param context 当前指向的节点<节点内容>如:environments
	 * @throws Exception
	 */
	private void environmentsElement(XNode context) throws Exception {
		if (context != null) {
			if (environment == null) {
				environment = context.getStringAttribute("default");
			}
			for (XNode child : context.getChildren()) {
				String id = child.getStringAttribute("id");
				// 循环比较id是否就是指定的environment
				if (isSpecifiedEnvironment(id)) {
					// 7.1事务管理器
					TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
					// 7.2数据源
					DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
					DataSource dataSource = dsFactory.getDataSource();
					Environment.Builder environmentBuilder = new Environment.Builder(id).transactionFactory(txFactory)
							.dataSource(dataSource);
					configuration.setEnvironment(environmentBuilder.build());
				}
			}
		}
	}

	// 8.databaseIdProvider
	// 可以根据不同数据库执行不同的SQL，sql要加databaseId属性
	// 这个功能感觉不是很实用，真要多数据库支持，那SQL工作量将会成倍增长，用mybatis以后一般就绑死在一个数据库上了。但也是一个不得已的方法吧
	// 可以参考org.apache.ibatis.submitted.multidb包里的测试用例
	// <databaseIdProvider type="VENDOR">
	// <property name="SQL Server" value="sqlserver"/>
	// <property name="DB2" value="db2"/>
	// <property name="Oracle" value="oracle" />
	// </databaseIdProvider>
	/**
	 * 解析databaseIdProvider元素<数据库厂商标识>
	 * @param context 当前指向的节点<节点内容>如:databaseIdProvider
	 * @throws Exception
	 */
	private void databaseIdProviderElement(XNode context) throws Exception {
		DatabaseIdProvider databaseIdProvider = null;
		if (context != null) {
			String type = context.getStringAttribute("type");
			// awful patch to keep backward compatibility
			// 与老版本兼容
			if ("VENDOR".equals(type)) {
				type = "DB_VENDOR";
			}
			Properties properties = context.getChildrenAsProperties();
			// "DB_VENDOR"-->VendorDatabaseIdProvider
			databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
			databaseIdProvider.setProperties(properties);
		}
		Environment environment = configuration.getEnvironment();
		if (environment != null && databaseIdProvider != null) {
			// 得到当前的databaseId，可以调用DatabaseMetaData.getDatabaseProductName()得到诸如"Oracle
			// (DataDirect)"的字符串，
			// 然后和预定义的property比较,得出目前究竟用的是什么数据库
			String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
			configuration.setDatabaseId(databaseId);
		}
	}

	// 7.1事务管理器
	// <transactionManager type="JDBC">
	// <property name="..." value="..."/>
	// </transactionManager>
	/**
	 * 解析transactionManager<事务管理器>
	 * @param context 当前指向的节点<节点内容>如:transactionManager
	 * @return TransactionFactory
	 * @throws Exception
	 */
	private TransactionFactory transactionManagerElement(XNode context) throws Exception {
		if (context != null) {
			String type = context.getStringAttribute("type");
			Properties props = context.getChildrenAsProperties();
			// 根据type="JDBC"解析返回适当的TransactionFactory
			TransactionFactory factory = (TransactionFactory) resolveClass(type).newInstance();
			factory.setProperties(props);
			return factory;
		}
		throw new BuilderException("Environment declaration requires a TransactionFactory.");
	}

	// 7.2数据源
	// <dataSource type="POOLED">
	// <property name="driver" value="${driver}"/>
	// <property name="url" value="${url}"/>
	// <property name="username" value="${username}"/>
	// <property name="password" value="${password}"/>
	// </dataSource>
	/**
	 * 解析dataSource<数据源>
	 * @param context 当前指向的节点<节点内容>如:dataSource
	 * @return DataSourceFactory
	 * @throws Exception
	 */
	private DataSourceFactory dataSourceElement(XNode context) throws Exception {
		if (context != null) {
			String type = context.getStringAttribute("type");
			Properties props = context.getChildrenAsProperties();
			// 根据type="POOLED"解析返回适当的DataSourceFactory
			DataSourceFactory factory = (DataSourceFactory) resolveClass(type).newInstance();
			factory.setProperties(props);
			return factory;
		}
		throw new BuilderException("Environment declaration requires a DataSourceFactory.");
	}

	// 9.类型处理器
	// <typeHandlers>
	// <typeHandler handler="org.mybatis.example.ExampleTypeHandler"/>
	// </typeHandlers>
	// or
	// <typeHandlers>
	// <package name="org.mybatis.example"/>
	// </typeHandlers>
	/**
	 * 解析typeHandlers<类型处理器>
	 * @param parent 父节点
	 * @throws Exception
	 */
	private void typeHandlerElement(XNode parent) throws Exception {
		if (parent != null) {
			for (XNode child : parent.getChildren()) {
				// 如果是package
				if ("package".equals(child.getName())) {
					String typeHandlerPackage = child.getStringAttribute("name");
					// （一）调用TypeHandlerRegistry.register，去包下找所有类
					typeHandlerRegistry.register(typeHandlerPackage);
				} else {
					// 如果是typeHandler
					String javaTypeName = child.getStringAttribute("javaType");
					String jdbcTypeName = child.getStringAttribute("jdbcType");
					String handlerTypeName = child.getStringAttribute("handler");
					Class<?> javaTypeClass = resolveClass(javaTypeName);
					JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
					Class<?> typeHandlerClass = resolveClass(handlerTypeName);
					// （二）调用TypeHandlerRegistry.register(以下是3种不同的参数形式)
					if (javaTypeClass != null) {
						if (jdbcType == null) {
							typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
						} else {
							typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
						}
					} else {
						typeHandlerRegistry.register(typeHandlerClass);
					}
				}
			}
		}
	}

	// 10.映射器
	// 10.1使用类路径
	// <mappers>
	// <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
	// <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
	// <mapper resource="org/mybatis/builder/PostMapper.xml"/>
	// </mappers>
	//
	// 10.2使用绝对url路径
	// <mappers>
	// <mapper url="file:///var/mappers/AuthorMapper.xml"/>
	// <mapper url="file:///var/mappers/BlogMapper.xml"/>
	// <mapper url="file:///var/mappers/PostMapper.xml"/>
	// </mappers>
	//
	// 10.3使用java类名
	// <mappers>
	// <mapper class="org.mybatis.builder.AuthorMapper"/>
	// <mapper class="org.mybatis.builder.BlogMapper"/>
	// <mapper class="org.mybatis.builder.PostMapper"/>
	// </mappers>
	//
	// 10.4自动扫描包下所有映射器
	// <mappers>
	// <package name="org.mybatis.builder"/>
	// </mappers>
	/**
	 * 解析mapper映射器
	 * @param parent 父节点
	 * @throws Exception
	 */
	private void mapperElement(XNode parent) throws Exception {
		if (parent != null) {
			for (XNode child : parent.getChildren()) {
				if ("package".equals(child.getName())) {
					// 10.4自动扫描包下所有映射器
					String mapperPackage = child.getStringAttribute("name");
					configuration.addMappers(mapperPackage);
				} else {
					String resource = child.getStringAttribute("resource");
					String url = child.getStringAttribute("url");
					String mapperClass = child.getStringAttribute("class");
					if (resource != null && url == null && mapperClass == null) {
						// 10.1使用类路径
						ErrorContext.instance().resource(resource);
						InputStream inputStream = Resources.getResourceAsStream(resource);
						// 映射器比较复杂，调用XMLMapperBuilder
						// 注意在for循环里每个mapper都重新new一个XMLMapperBuilder，来解析
						XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource,
								configuration.getSqlFragments());
						mapperParser.parse();
					} else if (resource == null && url != null && mapperClass == null) {
						// 10.2使用绝对url路径
						ErrorContext.instance().resource(url);
						InputStream inputStream = Resources.getUrlAsStream(url);
						// 映射器比较复杂，调用XMLMapperBuilder
						XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url,
								configuration.getSqlFragments());
						mapperParser.parse();
					} else if (resource == null && url == null && mapperClass != null) {
						// 10.3使用java类名
						Class<?> mapperInterface = Resources.classForName(mapperClass);
						// 直接把这个映射加入配置
						configuration.addMapper(mapperInterface);
					} else {
						throw new BuilderException(
								"A mapper element may only specify a url, resource or class, but not more than one.");
					}
				}
			}
		}
	}

	// 比较id和environment是否相等
	/**
	 * 比较environments中的default和environment中的id是否相等
	 */
	private boolean isSpecifiedEnvironment(String id) {
		if (environment == null) {
			throw new BuilderException("No environment specified.");
		} else if (id == null) {
			throw new BuilderException("Environment requires an id attribute.");
		} else if (environment.equals(id)) {
			return true;
		}
		return false;
	}

}
